Voodoo Lab Pedal Power MONDO - Manual (Page 11)

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About Isolation
Pedal Power MONDO has 12 isolated output sections. This is sometimes
referred to as “galvanic isolation” and means that there is no direct electrical
connection between each output. Similarly, when you power your effects with
batteries, they are also isolated because there is no electrical connection
between the batteries.
Most power supplies are not isolated. Their output jacks are simply bussed
together or use a daisy chain cable. This allows unwanted electrical current to
flow between the outputs, commonly called a ground loop. The result is added
noise. The isolated outputs of Pedal Power MONDO eliminate this noise.
Another benefit of isolation is that you can power both negative ground and
positive ground effects with Pedal Power MONDO. Negative ground effects are
by far the most common, however the Fuzz Face and Octavia are some well
known examples of positive ground circuits. Attempting to power positive ground
pedals together with negative ground pedals from a non-isolated power supply
will not work and may even damage the supply.
There are a couple of other tricks you can get from an isolated supply like Pedal
Power MONDO. You can use a special Y-cable (voltage doubler cable) which
connects two 9V outputs in series to provide an isolated 18V, or use the 12V
outputs to get 24V. Occasionally, a pedal requires a bipolar supply, using two
batteries for +9V and -9V. Isolated outputs work fine for this, non-isolated
supplies do not.
Voodoo Lab has been the pioneer of isolated power supplies for guitar pedal
effects since 1996.